apply_polygon: raster-cube instead of datacube

[katharinastarzer21]

Process ID:
apply_polygon

Describe the issue:
In the .json description of apply_polygon, some subtype values are still listed as "raster-cube", which should be updated to "datacube" to align with the version 2.0.0 -rc.1.

Proposed solution:
Replace "subtype": "raster-cube" with "subtype": "datacube" in the specified lines.

Additional context:
Link to the wrong lines:
https://github.com/Open-EO/openeo-processes/blob/master/proposals/apply_polygon.json#L15
https://github.com/Open-EO/openeo-processes/blob/master/proposals/apply_polygon.json#L47
https://github.com/Open-EO/openeo-processes/blob/master/proposals/apply_polygon.json#L66
https://github.com/Open-EO/openeo-processes/blob/master/proposals/apply_polygon.json#L106